Segovia was conquered by the Romans in the 1st century and became a military center. The Roman aqueduct, built without mortar, is a masterpiece of Roman engineering. Segovia has many other important monuments, like the Alcazar, a fortress, which dates from the 11th century, and numerous Romanesque buildings and churches which were built in the 12th and 13th centuries. Isabella the Catholic was proclaimed in 1474 queen of the kingdom of Castile in the Church of San Miguel, and it was through her support that Christopher Columbus was able to sail to the Indies using a western route, which led to the discovery of America in 1492.